Ok,
As this rooms PCs are windows PCs, joined to an Active Directory, I used AD, and auth works fine (because my organization's AD master did it with me).
I guess I needed some more configuration in env and advanced parameters to make it work.
I didn't have to do that with linux, as my PCs were LDAP auth based, and in access control, I just had to choose "default (local groups and users)", and not LDAP, as I have to with AD joined windows PCs.
I didn't test further ldap conf, as I finally don't need it
Answer this post could help other people with the same question, though